Cellular communications systems typically include multiple base stations for communicating with mobile stations in various geographical transmission areas. Each base station provides an interface between the mobile station and a telecommunications network. Mobile telephone systems are in use or being developed in which the geographic coverage area of the system is divided into smaller separate cells, it communicates with the network via a fixed station located in the cell. Mobile telephones belonging to the system are free to travel from one cell to another. When a subscriber within the same system or within an external system wishes to call a mobile subscriber within this system, the network must have information on the actual location of the mobile telephone.
Recently, the price of cellular telephone has been greatly reduced and become affordable to lots of people. It is common that a person owns more than one cellular phone. Some people even replace their cellular telephones as often as they replace their clothes or hairstyle. The cellular manufactures have to release new models with different appearances, function and styles more frequently so as to attract the attention of the buyer and occupy a favorable marketing share.